Semiconductor devices, such as silicon integrated circuit chips or other semiconductor devices, are subject to early failure during their life cycle. It is desirable to detect and eliminate the devices that are most prone to early failure prior to sending them to market. Additionally, it is desirable to identify the components of the semiconductor devices that cause the early failures so that they may be improved. Thus, producers of these devices have found it cost-effective to utilize burn-in systems to rigorously temperature stress the semiconductor devices while simultaneously powering them in order to test the reliability of the devices.
Burn-in test systems typically utilize burn-in boards to support a number of semiconductor devices to be tested. The burn-in test system powers the devices under test and exposes the devices to heat stress over an extended period of time. A determination of the reliability of the devices can be made based on the actual semiconductor die temperature during the test.
One option used by semiconductor manufacturers to detect the temperature of a device under test, is to incorporate a diode within the semiconductor device that is dedicated to temperature sensing. The dedicated temperature sense diode is accessed through two package pins, such as described in U.S. Pat. No. 5,359,285. Conventional techniques are used to establish the temperature of the device under test using the dedicated diode. In general, multiple currents are delivered to the dedicated temperature sense diode through the corresponding pins of the device. An accurate temperature reading can then be obtained for the device based on the applied currents and the voltage across the diode during application of the currents. One such conventional technique is described in U.S. Pat. No. 5,195,827.
The package pins dedicated to temperature sensing during burn-in testing generally serve no purpose after the burn-in testing is completed, as they are not input/output (I/O) pins, or pins that are connected to the core logic of the device. The benefit from the increase in cost, size and complexity of the semiconductor device due to the inclusion of the dedicated temperature sensing package pins and the temperature sense diode, is lost following burn-in testing. The added cost of including the dedicated temperature sensing package pins can be significant when the dedicated temperature sensing package pins constitute a relatively large percentage of the total available pins. As a result, some manufacturers are reluctant to include dedicated temperature sensing package pins in some semiconductor devices.
When the semiconductor devices do not include dedicated temperature sensing package pins, the temperature of the semiconductor device is estimated based on the temperature of the top of the package, which is detected by a temperature sensor that is external to the semiconductor device. However, the estimated package temperature can be inaccurate if the package-to-die thermal resistance is high and the semiconductor dissipates a large amount of power. Unfortunately, the power usage and thermal resistance values are generally not known at the burn-in testing stage of development.